AC / Heater stuck in hot temp control and high fan

[Plumber101010]

2015 WT Crew 4x4 3500 Duramax SRW.  Batteries were dead and tried to jump start but it took many times with my battery pack.

 

During which all of the computer stuff was flashing on and off a zillion times as engine dragged slowly then click click click and drag slowly and then click click click and yes, I got it started but all of the computer stuff went haywire and a dozen engine codes went off.

 

I cleared out all the codes and everything went back to normal. Except the manual controls for the Heater / AC  all became inoperative and none of the lights are on as well for each control knob and everything is stuck in the last used position, which is temperature control all the way to hot, the fan on high and blowing out floor vents.

 

This is bizarre to me as normally I would just think a fuse blew and replace it but since the fan is blowing and it’s coming out hot that means it can’t be a fuse I guess??

 

Never had this happen before and is clear over my head trying to figure out what could be the cause

[Jsdirt]

This is what you get when auto manufacturers load vehicles with 15 -30 separate computers. The days of old are long gone, unfortunately. Welcome to the world of GLITCHES.

 

Some of these newer vehicles require a computer reflash (reprogramming) whenever a battery is changed. I'm not aware of GM doing this (YET - more a Euro thing at present), but if they can make a buck off it, they'll do it.

 

I would make sure that battery is FULLY charged and in good condition, disconnect it, and let it sit overnight that way. Back in the day we used to touch the positive and negative cables together after they were disconnected to deplete any stored charge in the computer. These days I wouldn't dare do that, especially on anything built after 2006. Let it sit overnight, then reconnect everything in the morning ... BUT make sure to do it FAST. Don't let the cable bounce off and spark - touch it ONCE and HOLD there until you get the cable tight.

 

If this doesn't work, you're going to have to find a shop that does programming, or a mobile programmer - DON'T go to the dealer unless 100% covered under warranty. Sometimes a reflash will get the "stupid" out of the magic boxes. 

 

And if THAT doesn't work, don't be surprised if you have to replace the entire HVAC module AND have the new one programmed. This is the automotive world today, unfortunately.

Edited December 19, 2018 by Jsdirt

[Doug_Scott]

We're you using one of those handheld miracle battery boosting devices?  The ones I have seen have 12 to 10 gauge "wires" instead of proper battery cables. A diesel engine requires a lot more current than a gasoline engine does for cranking.  

Hopefully you have a proper battery charger, and if you do, charge the battery with both cables off.  You are going to have to take them off in order to clean them anyways. 

 

Why was the battery dead? 

[Plumber101010]

Yep!!!  Was using a power pack that’s not as powerful as it needs to be but I was in a rush to get somewhere and didn’t have time to put a slow charge to it. To make things worse I have a 200 hp tune so reflashing everything could cause some issues. I could bring it back to the guy who did the tune, he has one of those fancy $12,000 scanners that can go in and re-program things????

[Jsdirt]

You'd have to ask him - he'd probably have to reinstall everything back to stock, reflash the module, then redo the tune, I would think.

 

Did you try disconnecting the batteries from the truck, and letting them sit overnight that way?

[Plumber101010]

Not yet.  Mainly because it’s my only vehicle and I don’t have the time to wait the full 24 hours? I could do it now but can only let it sit a couple hours?  Think that will work?

 

I was reading another article about some kind of system where you put the key in, turn  it on but don’t start, then hook up the batteries and turn the key of,  blah blah do you think all that’s necessary?

[Doug_Scott]

Don't connect the battery up with ignition in the on position.  Computers don't take kindly to doing that. Just remove the negative cable first, the positive cable.  While they are off, it would be a good time to clean them.  If you have a battery charger, connect it up and charge it with the cables off for a couple of hours.  Then connect positive cable first, followed by the negative. 

[diyer2]

1 hour ago, Plumber101010 said:

Not yet.  Mainly because it’s my only vehicle and I don’t have the time to wait the full 24 hours? I could do it now but can only let it sit a couple hours?  Think that will work?

 

I was reading another article about some kind of system where you put the key in, turn  it on but don’t start, then hook up the batteries and turn the key of,  blah blah do you think all that’s necessary?

A couple hours will not do it!

A Digital Voltage Meter will confirm that.

New batteries is what I would do if they are more than 4 years old.

 

Edited December 19, 2018 by diyer2

[Plumber101010]

They are brand new, both a month old. But completely drained them to dead 1/2 dozen times now. Long story as to why but know why. So what are we trying to achieve by waiting 24 hours just so I know?  Is that how long it takes to reset the computer  because voltage is stored up somewhere?

Edited December 19, 2018 by Plumber101010

[Plumber101010]

I mean here’s the thing. Being my only vehicle it’s driven daily and I don’t for see any time in the next couple months that I can wait 24 hours. And it’s cold outside

 

Yes it’s stuck in heater but we all know what that means after 10 minutes you’re sweating your balls off lol

[Jsdirt]

You can try a couple hours, or an hour .. but if it doesn't work, you'll have to keep trying. 24 hours just kills all the variables and makes things easier. I'd try an overnight disconnect instead - you'll just have to remember to get up a half hour earlier in the AM.

 

Your basically just rebooting all the modules. They have capacitors in there that take time to power down. If any of them stay alive during the process, it will be like you never disconnected anything.

 

Would suck to pay $500 (just a guess  - could be more) for a new HVAC module plus $100 for programming (or more), only to find out a simple battery disconnect would've fixed the issue.

Edited December 19, 2018 by Jsdirt

[Plumber101010]

I gotcha. OK I will try overnight and update the results here in the morning!  Thanks everyone 

[Plumber101010]

Been couple hours. Can I just take my volt meter and attach to cables and see if showing any voltage??

[Plumber101010]

Ok here we go. Been 18 hours. Longest I can go. Let’s see what happens

[Jsdirt]

That should be good enough. Fingers crossed ...

[Plumber101010]

CRAP!!!  One guy just told me to make sure I don’t touch any of the controls for two minutes....now he tells me... lmao!  

 

It was dead and nothing happened but everything else came on but I did try to adjust the fan and turn the AC on after about 30 seconds but still nothing. Dang it!!! Any chance this could be a fuse related issue even though fan and temp control out working in the last position i used???